Optical character reader employing gated amplifiers



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mvsmons KLAUS w. OTTEN JOHN B. CHRISTIE a GERALD a. HOLLINS THEIR ATTORNEYS United States Patent 3,492,647 OPTICAL CHARACTER READER EMPLOYING GATED AMPLIFIERS Klaus W. Otten, Xenia, and John B. Christie and Gerald B. Hollins, Dayton, Ohio, assignors to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Filed Dec. 23, 1966, Ser. No. 604,413 Int. Cl. G06k 9/12 US. Cl. 340146.3 18 Claims ABSTRACT OF THE DISCLOSURE This reading machine employs a scanning device which scans an image area containing a data pattern to develop a signal that is sensed by a sensing device. The sensed signal is coupled to a number of operational amplifiers that are under control of a control means that serves to activate each operational amplifier only during selected sub-portions of the scan of the main signal area in correspondence with a plurality of sub-image areas of the main image area. The sub-image areas are selected to represent predetermined comparisons of the data pattern. A plurality of analog difference signals are then formed which are each a function of the difference between the sum of one set of operational amplifier output signals and the sum of a second set of operational amplifier output signals. The analog difference signals and the output signals of the operational amplifiers are then digitized and are combined in digital logical circuits to produce a digital recognition signal that represents the imaged data pattern.

The present invention relates in general to optical character recognition and in particular to optical character recognition readers that employ a number of subimage or mask areas to view selected portions of an image area.

The present invention involves a novel character recognition scheme which uses video-processing operational amplifiers that are associated with various sub-image areas to develop digital recognition signals which identify characters that are imaged in an image area.

A number of optical character recognition readers have been developed which utilize the best-match technique of character recognition. In the best-match technique, a number of masks are superimposed over an imaged character, and a set of video signal patterns are developed through such masks to represent the imaged character. In the best-match technique, the set of video patterns generated by the character under observation are matched to a particular character from an ideal set of characters according to the video patterns generated.

The reader of the present invention directly develops digital recognition signals from the video signals which are generated by the unknown imaged characters when various sub-image or mask areas are employed. The present recognition reader, therefore, does not require that the video signals that it develops be compared with signals which represent ideal characters.

The video signals which are generated immediately from the imaged character and the sub-image areas in the reader of the present invention are called the a functions. The digital signals which are developed from the a functions are designated as the A functions. Mathematically, the cm functions generated in the reader are described by:

ICC

where V(t) is a video signal derived from scanning an unknown character during the time interval d(l and R (t) is a binary function which symbolizes a mask or sub-image area so that either:

according to the value of the binary function R (t) during the time interval d(t A value of R (t)=l corresponds to a sub-image area, and the video signal from the character is used in forming the A function signal when R (t) -l. If R U) =0, the video signal received from the character is not used in forming the A function signal. The R (t) functions are implemented in the reader by gate circuits which are connected to the inputs of the video integrating amplifiers. The gate circuits allow the integrating amplifiers to process video information when R (1)=1, and they block video information to the amplifiers when R (t)=0.

A plurality of gated video integrating amplifiers are connected to a video pre-amplifier that is coupled to a photomultiplier pick-up tube in the preferred embodiment of the present invention. A light scanning beam from a scanner causes light reflection at the image area, the intensity of which varies according to the imaged character. An alternate embodiment of this invention employs characters which are stored in a cathode ray storage tube, and electronic scanning means are employed. The video integrating amplifiers all have individual gate control circuits, and therefore each amplifier is associated with an individual R (t) function. The R (t) function represents a particular sub-image area of the main image area, and the R (t) function has a value of one whenever the scan is traversing a portion of the associated sub-image area. Thus the video signal which is selectively coupled from the photomultiplier tube to a particular video integrating amplifier represents the video signal which is associated with a particular sub-image area.

The preferred embodiment of this invention also includes a video integrating amplifier which is gated open during scan of the total image area. The imaged character is normalized in size, by methods known in the art, in both the vertical and the horizontal directions in the preferred embodiment. The output of a video amplifier which is open during the scan of the whole normalized image area, therefore, represents the amount of the total image area which is covered by the imaged character, and this output is used as a normalizing signal, as will be described.

Although the preferred embodiment employs a normalization signal which is derived by integration of the video information signal over the total image area, it is apparent that other normalization signals may also be used; for example, an integrated summation of the video signal over only a part of the total image area may be used for normalization. The measurement of the maximum black signal that is received over the image area or the black signal received from a particular group of sub-image areas may also be used as normalization signals. Elimination of the normalization signal completely will affect the accuracy of the reader of the present invention to some extent when used with a large number of different font characters; however, a reader of a more limited accuracy is still achieved by the reader of the present invention even without using a normalization signal.

The output signals from the video integrating amplifiers which are coupled to the photomultiplier are selectively gated to form the analog (1,, function signals, each of which corresponds to a particular sub-image area. The various a function signals are compared with other a function signals, and the resulting comparison signals are analog signals which are called the b function signals.

The a function signals and the b function signals are applied to threshold detecting circuits which convert these signals into digital logic level A and E signals. In the preferred embodiment, the threshold level of the detecting circuits which transpose the a and the b signals into A and E signals utilizes a normalization signal which is derived by intergrating the video signal received over the total image area to insure that the A and the B function signals that are generated are normalized with respect to this video signal, for reasons which will be explained subsequently.

It is, therefore, an object of the present invention to provide an optical recognition reader that identifies an unknown character which is image in an image area by translation of video signals, which correspond to a plurality of sub-image areas, into a recognition signal, which is representative of the unknown imaged character.

It is another object of the present invention to provide digital conversion means that indicate whether a group of information signals is greater or smaller than a predetermined fraction of a normalization signal.

It is a further object of the present invention to provide digital conversion means that indicate whether the difference between one group of information signals and another group of information signals is greater or smaller than a predetermined fraction of a normalization signal.

Other object and features of the optical recognition reader of this invention will become apparent to those skilled in the art from the description, claims and drawings describing the present invention, wherein:

FIG. 1 is a diagrammatic illustration of the a and the A function signal generation portion of the reader.

FIG. 2 is a diagrammatic illustration of the two-dimensional register employed by the reader.

FIG. 3 is a schematic of a typical integrating circuit.

FIG. 4A is a diagrammatic illustration of a portion of the control gate logic of the reader for gate signals I through XVII.

FIG. 4B is a diagrammatic illustration of a portion of the control gate logic of the reader for gate signals XVIII through XXIII.

FIG. 5 is a sub-image area plot for sub-image areas XI, XII, XV, XVI, and XVII.

FIG. 6 is a sub-image area plot for sub-image areas I, II, III, IV, VI, VII, VIII, IX, X, and XIV.

FIG. 7 is a sub-image area plot for sub-image areas V, XIII, XVIII, XIX, XX, XXI, and XXII.

FIG. 8A is a diagrammatic illustration of the b and the B function signal generation portion of the reader for B function B through B FIG. 8B is a diagrammatic illustration of the b and the B function signal generation portion of the reader for B functions B, through B FIG. 8C is a diagrammatic illustration of the b and the B function signal generation portion of the reader for B functions B through B FIG. 9 is a schematic for the resistor voltage dividing networks for the B function Schmitt trigger circuits of FIGS. 8A, 8B, and 8C.

FIG. 10 is a schematic for the resistor voltage dividing networks for the A function Schmitt trigger circuit of FIG. 1.

FIG. 11 is a diagrammatic illustration of the recognition logic circuit for a 1.

FIG. 11a illustrates the logic symbols employed in the recognition logic circuits.

FIG. 12 is a diagrammatic illustration of the recognition logic circuit for a 2.

FIG. 13 is a diagrammatic illustration of the recognition logic circuit for a "3 FIG. 14 is a diagrammatic illustration of the recognition ogic ci c it f r a FIG. 15 is a diagrammatic illustration of the recognition logic circuit for a 5.

FIG. 16 is a diagammatic illustration of the recognition logic circuit for a 6.

FIG. 17 is a diagrammatic illustration of the recognition logic circuit for a 7.

FIG. 18 is a diagrammatic illustration of the recogni tion logic circuit for an 8.

FIG. 19 is a diagrammatic illustration of the recognition logic circuit for a 9.

FIG. 20 is a diagrammatic illustration of the recognition logic circuit for a 0.

FIG. 21 is a schematic of a typical b function summing amplifier.

FIG. 1 shows an unknown character, shown for example as the numeral 3, imaged on a normalized image area. Size normalization may also be achieved by elecby imaging a standard-size character in a fixed-size image area. Size normalization may also be achieved by electronic normalization of the unknown character on a cathode r-ay storage tube when electronic scanning means and cathode ray storage of the character to be read are employed and the size of the character is not standardized. The character image is normalized in the preferred embodiment of the present invention, but it is readily appreciated by one skilled in the art that the present invention is not necessarily limited to a normalized character image.

The scanner 30 produces a raster scan light beam pattern 32 across the image area 34. The scan control unit 36 supplies the X-scan or horizontal scan signal to the scanner 30 on the line 35, and the Y-scan or vertical scan signal is supplied to the scanner 30 on the line 39 by the Y-scan control unit 38. The scan control unit 38 applies a Start Sweep signal to the line 39 at the beginning of each scan, thereby setting the flip-flop 40. Setting of the flip-flop 40 supplies one input to the AND gate 42. The clock 44 is a repetitive square-wave signal generator which has an input terminal which is connected to the Y-scan control unit 38 by the line 33 to receive a sync signal from the Y-scan control unit 38 and an output terminal which is connected to the other input of the AND gate 42 through the line 45. When the flip-flop 40 is set, the set output of the flip-flop is applied to the line 43, both of the inputs to the AND gate 42 are satisfied periodically in accordance with the signal from the clock 44 on the line 45, and a repetitive square-wave signal is therefore effectively passed through the AND gate 42 to the register control line 46. The clock 44 is constructed to produce thirty-two square-wave pulses per sawtooth sweep output of the Y-scan control unit 38. At the end of the desired Y sweep signal, an End of Sweep signal is ap plied to the line 41 by the Y-scan control unit 38, thereby resetting the flip-flop 40 and opening the AND gate 42 to prevent additional clock pulses from being applied to the register control line 46.

The pulses on the register control line 46 are used as counting pulses by a pair of registers which are used to electrically generate the sub-image areas of the preferred embodiment of this invention. FIGS. 5, 6, and 7 are representations of the sub-image areas of the preferred embodiment of this invention. The sub-image areas that are formed in the preferred embodiment of the present invention are presented as combinations of rectangles for ease of implementation, but it is obvious that other forms of sub-image areas could be used with the reader of the present invention; for example, photo-masks may be employed to form the sub-image areas. The boundaries of the various sub-image areas of the preferred embodiment are controlled by a plurality of gates, shown on FIGS. 4A and 4B. Inputs to the gates are derived from the various stages of the y and x registers 48 and 50 of FIG. 2. The y-register 48 has the set input of its first flip-flop stage, 250 connected to the register control line 46. The set in-. put of the first flip-flop stage 257 of the J -register 50 is 

